The present invention is generally directed to an apparatus and method for optimizing performance of multi-circuit heat exchangers. As used herein, “heat exchanger” means a device built for relatively efficient heat transfer between a first medium and a second medium, the first medium being a fluid constrained in a conduit having a wall, the second medium being a fluid or a non-fluid, and if the second medium is a fluid, then the first medium and the second medium are separated by at least the conduit wall so that the first medium and the second medium do not come into contact with one another. A “multi-circuit” heat exchanger, as used herein, means a single heat exchanger having multiple fluid conduits (circuits) into which a flow of a fluid is subdivided while flowing from one common point to another common point, heat from another medium of the heat exchanger being transferred to or from the fluid while the fluid passes through the multiple fluid conduits.
Heat exchangers are used in a variety of applications. A very abbreviated list of some of the ways in which heat exchangers are used includes transferring heat from semiconductors to a cooling fluid, transferring heat in heating, ventilation, air conditioning, and/or refrigeration systems (“HVACR systems”) as part of a process to warm or cool a location, and transferring heat in industrial processes such as those used in electrical power plants, chemical plants and oil refineries.
For example, a typical function of one type of HVACR system is to heat or cool air to a more comfortable temperature by manipulating the transfer of heat. In particular, an air conditioning system may contain a cooling coil that absorbs heat from hot air to lower the air's temperature. Similarly, a heating system may utilize a heated gas or liquid to transfer heat to cold air to increase the air's temperature.
Heat transfer from or to a medium may be effected within such HVAC systems by the use of a working fluid or refrigerant, such as ammonia, R134a (tetrafluoroethane), or similar fluids. These working fluids are generally capable of changing state under various conditions of temperature and pressure. With each change of state, the working fluid either accepts energy or gives up energy. As a result, this energy is either removed or added to the medium, respectively, so that a cold medium may be heated or a hot medium may be cooled.
In the following example, the working fluid is a first fluid and the medium to be cooled is air, a second fluid. A heat exchanger is utilized to transfer heat between the first and second fluids while preventing intermixing of the two fluids.
In a conventional air conditioning system, the working fluid generally moves in the following cycle of operation: (1) from a compressor; (2) to a condenser; (3) through an expansion valve; (4) to an evaporator; and then (5) back to the compressor. As an example of a typical air conditioning system, the working fluid enters the compressor as a low temperature gas at about 65 degrees F. and leaves the compressor as a high temperature gas at about 150 degrees F. The working fluid then enters the condenser. Within the condenser, which is a heat exchanger, the working fluid thermally communicates with, and gives up heat to without intermixing with, surrounding cooler air or other cooler medium, and the working fluid is converted from a high temperature gas into a cooler liquid of about 90 degrees F. The working fluid then passes through an expansion valve to a region of low pressure. As a result, the working fluid begins to change state from a liquid to a low temperature gas of about 45 degrees F. The working fluid then flows through the evaporator, which is another heat exchanger, where the working fluid thermally communicates with, and absorbs heat from without intermixing with, the hot second fluid (air) flowing through another part of the evaporator. As heat is transferred from the hot second fluid to the working fluid, the hot second fluid is cooled, and the working fluid is heated to become a gas of about 65 degrees F., ready for return to the compressor. When the second fluid is a gas, such as the air in this example, the second fluid may be dehumidified as part of this process.
According to one aspect of the invention, this invention relates to a method for optimizing performance of a heat exchanger having multiple fluid circuits through which respective streams of a first fluid pass from a stream inlet to a stream outlet to transfer heat to or from a second medium. The method includes, as a first step, dividing the fluid circuits into at least two groups by identifying at least one group of the fluid circuits that perform similarly according to at least one selected performance criterion. A second step includes providing a respective valve for at least the identified group, which valve is in fluid communication with of all the streams of the associated group so as to be able to control the flow of fluid through the streams of the associated group in parallel. A third step, which may be performed before the second step, includes providing a respective sensor for at least the identified group, which sensor generates a signal representative of a parameter of the first fluid in the associated group. A fourth step includes operating each respective valve based at least in part upon the signal generated by the associated control sensor to separately control the flow of the first fluid though the associated group. According to another aspect, the invention also relates to a heat exchanger structure optimized by this method.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.